Chemical Mechanical Polishing (CMP) is a known means of planarizing semi-conductor layers which are built up on a silicon wafer substrate. Integrated circuits are typically formed on these substrates by sequential deposition of conductive, semi-conductive, or insulative layers. After each layer is deposited, an etching process is employed to create circuitry features on the silicon wafer. Through this sequential deposition and etching process, the outer most surface of the substrate becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of integrated circuitry fabrication therefore necessitating intermediate planarization steps in the process.
CMP typically utilizes an abrasive slurry dispersed in solution in combination with mechanical and chemical action along a surface of the wafer. One type of CMP polishing system has a rotatable circular platen or table on which a polishing pad is mounted. A multi-head or single head polishing device is positioned above the table. The polishing device has either a single or multiple rotating carrier heads to which wafers can be secured typically through the use of vacuum pressure or other securing methods. The platen is rotated and an abrasive slurry dispersed onto a polishing pad of the platen. Once the slurry has been applied to the polishing pad, the rotating carrier heads move downward to press corresponding wafers against the polishing pad. As the wafers are pressed against the polishing pad, the surface of the wafer is mechanically and chemically polished. As a result of both previous semiconductor operations and CMP processing, the finish will include undesirable aspects such as defect counts and cleanliness of the polished surface. The effectiveness of a CMP process may be measured by its polishing rate, and by the resulting finish and flatness of the substrate surface. The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and the pad, and the force pressing the substrate against the pad.
It is desirable to maximize the effectiveness of the CMP process by increasing the polishing rate and improving the resulting finish and flatness of the substrate surface. Retaining rings secured to the carrier have been developed to improve the resulting finish and flatness of the substrate surfaces. The flatness and planarity of the ring is critical to maintaining finish and flatness of the processed wafer. For example, U.S. Pat. No. 6,251,215 teaches a carrier head having a substrate mounting surface and a retaining ring to maintain a substrate beneath the mounting surface during polishing. The retaining ring is formed of two parts which include a lower portion having a bottom surface for contacting a polishing pad during polishing and an upper portion which is secured to the carrier head. The upper portion is formed of a material which is more rigid than the material of the lower portion. The rigid upper portion is said to be advantageous because it contributes to resulting flatness and finish of the substrate near its edges. This upper portion is therefore precision machined to be very flat and planar. It is desirable to have a flat ring pressing on the polishing pad to avoid flatness variations in the polished wafer. The lower portion wears during operation due to its contact with the polishing pad and is therefore a consumable in the process. The retaining ring as taught by this reference may be refurbished by replacing the lower portion upon wear.
Several problems exist in that this refurbishing process is time consuming and costly. During this refurbishing process the spent worn lower portion is removed from the relatively expensive precision machined upper portion and a new lower portion is applied generally using an adhesive. The application process involves steps to ensure flatness and planarity of the lower portion especially along its pad engaging surface. Other problems arise with refurbishing in tracking parts as well as the potential for cross-contamination of precision machined upper portions from copper metal system fabs coming in contact with those from non-copper metal system fabs.